Pharmacological properties of pempidine (1:2:2:6:6-pentamethylpiperidine), a new ganglion-blocking compound

Pempidine (1:2:2:6:6-pentamethylpiperidine) is a long-acting ganglion-blocking compound which is effective by mouth. By intravenous injection it has a similar potency to hexamethonium on the preganglionically stimulated nictitating membrane of the cat. The compound blocks the effects of intravenous nicotine and of peripheral vagal stimulation on the blood pressure; it also causes dilatation of the pupil after removal of the sympathetic innervation. On the guinea-pig ileum, the predominant effect of the compound is to inhibit nicotine contractions. Pempidine is well absorbed from the gastro-intestinal tract as judged by (a) the low ratio (6.9) of oral to intravenous toxicities, (b) the rapid development of mydriasis in mice after oral administration of small doses, and (c) the rapid onset of hypotension when the compound is injected directly into the duodenum of anaesthetized cats. Other actions include neuromuscular paralysis of curare-like type when large doses of the compound are injected intravenously and central effects such as tremors which occur with near toxic doses. In cats with a low blood pressure, large intravenous doses have a slight pressor action.

PARTICIPATION OF AN UNUSUAL GANGLIONIC PATHWAY IN THE MEDIATION OF THE PRESSOR EFFECT OF PHYSOSTIGMINE IN THE RAT

In spinal rats physostigmine failed to produce a pressor response even after treatment of the animals with hexamethonium, whereas noradrenaline, McN-A-343 (4-(m-chlorophenylcarbamoyloxy)-2-butynyltrimethylammonium chloride) and AHR602 (3-acetoxy-1-benzyl-1-methylpyrrolidinium bromide) all produced large pressor effects. In rats anaesthetized with urethane, hexamethonium completely abolished the pressor effect of dimethylphenylpiperazinium but only partially blocked the pressor response to physostigmine; pressor effects of noradrenaline, McN-A-343 and AHR602 were potentiated. Combined treatment with hexamethonium and atropine and with hexamethonium and cocaine, however, completely abolished the pressor effect of physostigmine; simultaneously the pressor effects of McN-A-343 and AHR602 as well as of dimethylphenylpiperazinium were also blocked. P-286 (N-diethylaminoethyl-N-isopentyl-N'N'-di-isopropylurea) produced an early and a late block of the pressor effect of physostigmine; the initial block was due to an adrenergic blocking action while the late block was probably due to a dual action of the drug in abolishing the effects of both the nicotinic and non-nicotinic ganglion stimulants. Pressor responses to physostigmine, McN-A-343, AHR602 and dimethylphenylpiperazinium were abolished immediately after ganglion-blocking doses of nicotine. It is suggested that an unusual ganglionic pathway participates in the mediation of the pressor response to physostigmine in the rat, especially when the established ganglionic pathways are blocked.